The present invention relates to an optical disc manufacturing apparatus for manufacturing optical discs such as digital video/versatile discs (hereinafter referred to as DVD) adopting particularly a bonding method.
When two plate shaped substances are stuck together using UV curable composition as adhesive, UV curable radical polymerization composition has heretofore been applied to surfaces to be bonded uniformly by a spin coating method, a screen printing method and the like, which have been existing technologies, and the surfaces to be bonded have been superposed on another, so as to be opposite, followed lower by curing the UV curable composition by irradiating ultraviolet rays continuously tinuously emitting light thereonto.
A high pressure mercury lamp, a metal halide lamp, a mercury-xenon lamp and the like have heretofore been used as an ultraviolet irradiation source. In such methods, there has been a problem that heat is apt to be caused owing to continuous light emission of the lamps and the heat has adverse effects on deformation of the plate shaped substances and mechanical properties thereof.
Furthermore, in the lamps of such lampes which emit light continuously, since it takes usually a time of more than several minutes until a light emission is stabilized lized after turning on the lamp, turning the lamp off/on is not easy. Accordingly, when the manufacturing is carried out continuously, the lamp must be kept turned on. Assuming that a time (cycle time of a production) required for bonding performed formaed one time (one cycle) be five seconds, and a time required for an ultraviolet irradiation radiation of five seconds be two seconds, the remaining three seconds are consumed uselessly wasting energy.
Furthermore, in the case where the two plate shaped substances are stuck together using the UV curable composition as the adhesive, when at least one of the plate shaped substances offers permeability to ultraviolet light, a severe problem does not occur. However, when the plate shaped substance attenuates an ultraviolet intensity, problems occur.
Specifically, the foregoing DVD and the like have a problem that because of the existence of an Al thin layer or the like in discs, the ultraviolet intensity is significantly attenuated by the thin layer and the layer until ultraviolet rays reach a bonding layer using the foregoing UV curable radical polymerization composition as the adhesive, so that curing-bonding with a high efficiency cannot be performed.
In addition, when it is intended to expedite the cure, lamp equipment having a large capacity is necessary, leading to an inevitable increase in the cost of products. Moreover, use of the lamp having a large capacity causes also a problem producing much conductive heat and radiation heat from the lamp, and a disc tends to be deformed. formed. In order to prevent this, cooling equipment around the lamp is additionally necessary, and the whole of the apparatus has been obliged to be large in size and more intricate.
On the contrary, when it is intended to perform ultraviolet curing with small capacity of the lamp equipment, though the ultraviolet curing is possible, a radiation time of several tens of seconds or more is required, so that the ultraviolet curing has been obliged to be poor in practicability.
A bonding method of a disc for solving the foregoing problems has been proposed in Japanese Patent Application Laid-Open No. 9-193249. Specifically, the bonding method of the disc disclosed in Japanese Patent Application Laid-Open No. 9-193249 has a feature in that ultraviolet rays are not radiated continuously but the ultraviolet rays are radiated in pulses. The method to radiate the ultraviolet ray continuously is the epoch-making one that can restrain power consumption for the ultraviolet radiation and increase the number of plate shaped substances to be stuck per unit of time, and can prevent a warp of the disc from occurring after sticking, compared to the case where the ultraviolet ray is continuously radiated.
Incidentally, there is also the following problem in the method by the flashing ultraviolet radiation. Specifically, when objects to be bonded is a DVD, for reasons of a structure of the DVD, an ultraviolet ray passes through an Al film which offers poor permeability to ultraviolet ray and reaches UV curable composition to cure this compound. Accordingly, when the Al film is thick by a product specification, a curing efficiency is deteriorated. Moreover, among the DVDs, for a DVD-RAM in which a film, for example, a ZnSxe2x80x94SiO2 film exists, through which ultraviolet rays cannot pass substantially, such a method cannot be adopted, in which the ultraviolet ray is radiated onto UV curable composition existing on sticking planes of two discs to cure the UV curable composition and bond the sticking planes to each other.
An effective bonding method against these problems has been disclosed in Japanese Patent Laid-Open No. 9-69239. The method stated in Japanese Patent Laid-Open No. 9-69239 has a feature in that UV curable cationic composition offering delayed action is used compared to the conventional method in which the UV curable radical polymerization composition has heretofore been used as the adhesive. To be more specific, the UV curable cationic composition is coated on the entire surface of one disc to be stuck, and ultraviolet is radiated onto the UV curable cationic composition after coating thereof Thereafter, the one disc is superposed on the other disc that is a sticking object, and then the UV curable cationic composition is hardened by compressing them to each other.
The method using the UV curable cationic composition stated in Japanese Patent Laid-Open No. 9-69239 is effective one in which bonding is possible when the Al film is thick or even in the DVD-RAM in which the ZnSxe2x80x94SiO2 film and the like allowing no ultraviolet to pass therethrough substantially stantially exist.
However, also in the method stated in Japanese Patent Laid-Open No. 9-69239, points to be further improved were found out. In other words, in the method in which the ultraviolet is radiated after the UV curable cationic composition position is coated on the disc substrate, though the ultraviolet radiation is required quired only for the UV curable cationic composition essentially, the ultraviolet is radiated also onto the disc substrate formed of polycarbonate and the like inevitably. Such unnecessary ultraviolet radiation onto the disc substrate is apt to cause thermal deformation in the disc substrate such as the DVD having a thickness of 0.6 mm due to heat from a lamp that is an ultraviolet light source.
Moreover, in the curing of the UV curable cationic composition, polymerization is disturbed by humidity of the air. Accordingly, the UV curable cationic composition protruding from an outer periphery of the disc after the superposition is sticky owing to delay of the curing. In addition, some measures must be taken to prevent deformation of the UV curable cationic composition and slippage of the two disc substrates from each other. In the DVD, though it is required for a deflection angle of the disc to be equal to a predetermined value or less according the standard, it is not clear with what measure the deflection angle can be fit in a predetermined range.
Accordingly, the subject of the present invention is to provide an optical disc manufacturing apparatus capable of manufacturing an optical disc having less air bubble trapping and suppressed unevenness in curing even when the UV curable cationic composition is used, and preventing a deformation of the disc due to conductive heat and radiation heat from a lamp that have been considered to be a problem in the conventional methods.
The inventor of this application made investigations to solve the foregoing subjects, and obtained the following knowledge. Specifically, since an ultraviolet ray is radiated onto a disc substrate inevitably in the conventional methods in which ultraviolet radiation is performed after a UV curable cationic composition is coated on the disc substrate, the inventor examined to coat the UV curable cationic composition on the disc substrate after the ultraviolet radiation. In other words, the inventor obtained knowledge that the UV curable cationic composition should be coated on the disc substrate after the ultraviolet ray is radiated onto the UV curable cationic composition in a place where the ultraviolet ray is not radiated onto the disc substrate or where the disc substrate is not affected thermally even if the ultraviolet is radiated.
Then, as a concrete technique to radiate the ultraviolet onto the UV curable cationic composition before this compound is coated on the disc substrate, the inventor conclude that the ultraviolet should be radiated in a space where the UV curable cationic composition falling in the air until it reaches the disc substrate. Specifically, this is because a sufficient ultraviolet radiation amount can be secured if diameters of the UV curable cationic composition falling are made to be small.
An optical disc manufacturing apparatus of the present invention realizes the above described methods based on the knowledge obtained, and the optical disc manufacturing apparatus of the present invention comprises: a nozzle for ejecting UV curable cationic composition; ultraviolet radiation means for radiating ultraviolet while the UV curable cationic composition falling from the nozzle reaches a disc substrate; and superimposing means for superimposing the two disc substrate so as to allow faces thereof onto which the UV curable cationic composition falls to be opposite to each other, thus making one disc.
Furthermore, as a whole of the apparatus, provided are a disc substrate taking-out area for taking out a plurality of disc substrates one by one from a disc holder which holds them in a stacked state, the foregoing nozzle and the foregoing ultraviolet radiation means, and provided are a disc preparation area for sticking the two disc substrates taken out together interposing the foregoing UV curable cationic composition therebetween, thus obtaining one disc, a disc checking area for checking the obtained disc, and a disc stacking region for stacking the foregoing disc holder with the discs after completion of checking.
Here, the fall of the UV curable cationic composition may be performed by dropping or by allowing this compound to fall continuously in such a manner that thick malt syrup falls stringily.
In the apparatus constituted as above, since the ultraviolet is previously radiated onto the UV curable cationic composition and thereafter the compound is spread on the disc substrate, air is not trapped therein, and the disc without unevenness in curing can be obtained. Specifically, the ultraviolet is radiated while the UV curable cationic composition falls from the nozzle to the disc substrate, so that the ultraviolet ray can be radiated onto the inside thereof uniformly, unevenness in curing does not occur as a result even in a method allowing the UV curable cationic composition to fall so as to form a ring shape, such as a spin coater method and the like, and an air bubble trapping prevention effect is also exerted. In addition, since sticking is performed without direct radiation of the ultraviolet ray onto the surface of the disc substrate, deformation of the disc after sticking can be avoided.
By the way, in the present invention, the UV curable cationic composition made from UV curable cationic resin (epoxy resin) and cationic polymerization photoinitiator is used. For this compound, the degree of cure is not saturated immediately after the ultraviolet radiation but saturated substantially after the passage of a predetermined time (such nature thereof is called a delayed action), unlike the degree of cure for ordinary UV curable composition is saturated substantially at approximately the same time as the ultraviolet radiation. Specifically, there is a time until the degree of cure is saturated after the ultraviolet radiation, that is, there is a pot life. The UV curable cationic composition containing the UV curable cationic resin and the cationic polymerization photoinitiator as essential ingredients should be made to be substantially solventfree liquid for the sake of its easiness of falling to the disc substrate. It is more preferable to select the composition of the compound so that the compound itself and its cured bonding layer become transparent.
A viscosity of the compound set to 50 to 10000 mPaxc2x7s at a temperature of 25xc2x0 C., more preferably 100 to 1000 mPaxc2x7s. A time during after the ultraviolet radiation is completed until the degree of cure saturates and an absolute value of the saturation degree of cure, are adjusted depending on kinds and the ratio in weight of the UV curable cationic resin and the cationic polymerization photoinitiator combined with the resin. For example, the time is adjusted to 3 to 30 minutes, preferably 5 to 25 minutes, more preferably 5 to 15 minutes, and most preferably 5 to 10 minutes.
As UV curable cationic composition, all of known compounds can be used, and epoxy resins containing cationic polymerization photoinitiator fall into this. As the cationic polymerization photoinitiator, sulfonium salt, iodonium salt, diazonium salt and the like are used.
As examples of the iodonium salts, there are the following.
Diphenyl iodonium hexafluorophosphate, diphenyl iodonium hexafluoro antimonate dipheny liodium tetrafluoro borate, diphenyl iodonium tetrakis(pentafluorophenyl)borate, bis(dodecylphenyl)iodonium hexafluorophosphate, bis(dodecylphenyl)iodonium hexafluoroantimonate, bis(dodecylphenyl)iodonium tetrafluoroborate, bis(dodecylphenyl)iodonium tetrakis(pentafluorophenyl) borate, 4-methylphenyl-4-(1-methylethyl)phenyliodonium hexafluorophosphate, 4-methylphenyl-4-(1-methylethyl)phenyliodonium hexafluoroantimonate, 4-methylphenyl-4-(1-methylethyl)phenyliodonium tetrafluoroborate, and 4-methylphenyl-4-(1-methylethyl)phenyliodonium tetrakis(pentaflurophenyl)borate can be mentioned.
The epoxy resin may be any of bisphenol-A-epichlorohydrin type, alicyclic epoxy, long chain fatty group type, bromide epoxy resin, glycidyl ester type. glycidyl ether type, heterocyclic type series and the like. As a preferable epoxy resin, there are xe2x80x9cEPICLON 850Sxe2x80x9d produced by DAINIPPON INK AND CHEMICALS, Inc., and xe2x80x9cDENACOL EX-313xe2x80x9d, xe2x80x9cDENACOL EX-314xe2x80x9d, xe2x80x9cDENACOL EX-321xe2x80x9d, xe2x80x9cDENACOL EX-421xe2x80x9d, xe2x80x9cDENACOL EX-512xe2x80x9d and xe2x80x9cDENACOL EX-521xe2x80x9d produced by Nagase Chemicals Ltd.,
As the epoxy resin to produce a DVD-RAM, for example, it is preferable to use the one showing contents of free chlorine liberated and chlorine ions which are equal to zero or value as close to zero as possible, to prevent to the utmost a change of properties with time in an information recording layer made of a metal film which reflects almost ultraviolet. It is recommended to set an amount of chlorine to be 1 weight % or less and preferably 0.5 weight % or less.
A ratio of the UV curable cationic resin to the cationic polymerization photoinitiator in weight can be selected based on the above descriptions, and the ratio is 0.1 to 20 part by weight per 100 part by weight of the UV curable
If the ultraviolet ray is radiated also onto an ejection opening of the nozzle in radiating the ultraviolet onto the falling UV curable cationic composition, the UV curable cationic composition is cured at the ejection opening of the nozzle, and this causes troubles such as a reduction in an ejection amount and blocking of the ejection opening. To prevent such troubles, in the apparatus of the present invention, the ejection opening is protected by a prevention cover against ultraviolet exposure. It is not always required for the ultraviolet exposure prevention cover to cover the entire periphery of the ejection opening. Its shape is optional, as long as the object to protect the ejection opening from the ultraviolet ray is achieved.
The ultraviolet radiation is performed so that an amount of the ultraviolet radiation onto the falling UV curable cationic composition during the falling of this compound from the nozzle to the disc substrate is ordinarily 50 to 500 mJ/cm2 and preferably 100 to 400 mJ/cm2.
The total thickness of a bonding layer made of the UV curable cationic composition containing the UV curable cationic resin and the cationic polymerization photoinitiator is not especially limited, but ordinarily, the total thickness thereof is set to 15 to 60 xcexcm, and preferably 20 to 55 xcexcm.
The following technique should be adopted to superpose the two disc substrates interposing the UV curable cationic composition therebetween.
Specifically, the UV curable cationic composition that has been subjected to the ultraviolet radiation previously is coated on one disc substrate in the form of a ring. Thereafter, when the other disk substrate is superimposed on the one disc substrate, it is recommended that the two disc substrates are superimposed not in the state of being parallel with each other from the beginning, but the two disc substrates are superimposed in a state where the two disc substrates are tilted from each other at first, then gradually made to be close to a cationic resin, and preferably 0.2 to 5 part by weight per 100 part by weight thereof.
Note that to more effectively use waves of a near ultraviolet region and a visible region in a wavelength region of an ultraviolet light source, photosensitizer publicly known and commonly used can be used together with these compounds. As the photosensitizer used at this time, anthracene, phenothiazine, benzyl methyl ketal, benzophenone, acetophenone and the like are, for example, enumerated.
To radiate the ultraviolet ray onto the UV curable cationic composition falling from the nozzle, ultraviolet radiation means may be provided on the side of the UV curable cationic composition falling, and as the light source for the ultraviolet radiation, known lamps such as a xenon lamp, a xenon-mercury lamp, a metal halide lamp, a high pressure mercury lamp, a low pressure mercury lamp and the like may be used.
To radiate the ultraviolet ray onto the UV curable cationic composition falling more uniformly, it is satisfactory to make diameters of the falling UV curable cationic composition small by reducing a diameter of the nozzle.
Moreover, it is also effective to radiate the ultraviolet ray onto the falling UV curable cationic composition from all directions. As concrete means for radiating the ultraviolet ray onto the falling UV curable cationic composition from all directions, it is conceived that a plurality of ultraviolet radiation means are provided around the falling UV curable cationic composition and the ultraviolet ray is radiated thereonto. However, when the falling UV curable cationic composition is surrounded by reflection plates and the ultraviolet ray is radiated onto the inside of the reflection plates surrounding the compound, the plurality of ultraviolet radiation means need not to be provided. Accordingly, energy saving and space saving can be achieved. desired distance, and thereafter the two disc substrates are allowed to be parallel with each other.
By adopting the above described method, compared to the method superpose the two disc substrates after setting the two disc substrates to be parallel with each other, reduction in air bubble trapping is possible. Moreover, it is desirable that when a gap between the two disc substrates is made to be small, a control is performed so as to approach in a unit of micron per one second, and the approach is performed intermittently.
Furthermore, in the present invention, the disc substrates to be stuck are made of either a material which allows hardly the ultraviolet ray to pass therethrough or a material which does not allow the ultraviolet ray substantially to pass therethrough. In fact, the disc substrates are not but made of a single material, also sometimes made of a composite material containing materials which allows the ultraviolet ray fully to pass and materials which hardly or substantially does not allow the ultraviolet ray to pass therethrough. As an example of these, there is DVD-10, DVD-18 having a thick metal film of such as the foregoing Al and the like among the DVD-ROM, or DVD-RAM.
In some cases, when the two disc substrates make DVD-ROM, at least one is a disc substrate having an information recording layer on an ultraviolet permeability substrate, and the other disc substrate does not have the information recording layer. Specifically, with reference to the discs which are the object of the present invention, there are a case where the two disc substrates have the information recording layer respectively and a case where though one disc substrate has the information recording layer, the other disc substrate does not have the information recording layer. In any case, the disc substrates have a thickness ranging from 0.3 to 1 mm usually.
As the disc substrates, any material which has been publicly known and commonly used can be used, for example, heat resistance thermoplastic synthetic resin such as acryl, polycarbonate and amorphous polyolefin are enumerated. The information recording layer is constituted by providing irregularities corresponding to recording information on one surface of the foregoing substrate, and laminating a metal film thereon.
In the present invention, though UV curable cationic composition can be coated directly on a metal film typified by a semi-reflection film and a reflection film then spread, it is also possible that the conventional UV curable composition adjusted so as to prevent as possible a change of properties with time in the metal film, as described above, is previously spread on this metal film and cured, and then the UV curable cationic composition may be coated, spread and cured on a protection layer made of a cured substance thereof. It should be preferable that a thickness of the protection film is set to 5 to 20 xcexcm in total. In this case, each protection film of the first and second disc substrates is bonded with each other by the UV curable cationic composition.
As the foregoing metal film, the one is preferably used, which is capable of reflecting visible light adopted for reading out the recording information, with a high efficiency, and identifying the foregoing irregularities accurately. A film reflecting the visible light with a high efficiency also reflects generally ultraviolet rays with a high efficiency.
As this metal film, Al, Ni, alloys made of these metals and the like are enumerated, which satisfy conditions that a visible light reflectance ranges from 80 to 100%, and a transmittance of ultraviolet rays across all over the wavelength regions thereof exceeds 0% and is equal to 10% or less, preferably exceeds 0 and is equal to 0.5% or less. Moreover, in discs according to standards called DVD-9 and DVD-18, a film called a semi-reflection film made of, for example, gold, which is a material offering a light transmittance ranging from 70 to 82%, is formed.
The DVD-RAM has a characteristic layered structure which is different from that of the above described DVDs. As an example of the DVD-RAM, the one having a following structure is known, that is, two disc substrates prepared such that a ZnSxe2x80x94SiO2 layer, a GeSbTe layer, a ZnSxe2x80x94SiO2 layer, an Al alloy layer and a protection layer are sequentially laminated on each substrate made of polycarbonate, are stuck to each other with their protection layer sides facing to each other, by using curing adhesive.
By the way, to stick the disk substrates in the foregoing manufacturing apparatus, the two kinds of disc substrates must be taken out from an inventory location one by one. At this junction, in view of spaces on production lines, the disc substrates are stored in a state of being stacked. When objects like the disc substrate having a smooth surface and a thin thickness are stacked, adhesive forces such as vacuum adsorption forces and electrostatic forces are apt to be generated between the disc substrates. If such adhesive forces exist, a disc substrate to be taken out is taken out with other disc substrates attached thereto, in spite of trying to take out the disc substrates one by one, resulting in taking out two or more disc substrates at one time.
When only one plate shaped substance is taken out from a plurality of stacked plate shaped substances such as the disc substrate, and transported to a next step, the following methods have been heretofore adopted to prevent taking-out of two or more disc substrates.
(1) a spacer is previously inserted between the plate shaped substances that is an object to be processed.
(2) ionized air for removing static electricity is blown from the side face of the stack of plate shaped substances.
In the method (1) in which the spacers for separating the plate shaped substances, which have a small size, are inserted between the stacked plate shaped substances, adhesive force due to electrostatic force and vacuum adsorbability are reduced to a large degree, and it is possible to certainly prevent the taking of the two or more plate shaped substances at a time. However, when the spacers are inserted in the above described manner, the spacers of the number equal to the number of the plate shaped substances are necessary, as well as means for inserting the spacers and means for removing the spacers are necessary, resulting in reducing throughput in the production significantly.
Moreover, like the method (2), when the ionized air is blown at the side of the stack of plate shaped substances, by supplying the ionized air from a small gap between the plate shaped substances stacked, the electrostatic adhesive force between the plate shaped substances is reduced, and the taking of the two or more disc substrates can be prevented. However, when the surfaces of the plate shaped substances are smooth mutually and scarcely making gaps on the sides of the stacked plate shaped substances, or when the vacuum adsorbability is strong, an ion neutralizing action does not work even if the ionized air is blown, and secure effects cannot be sometimes obtained. In addition, in the case where the ionized airs is blown, a costly ionized air generating apparatus and a supply source of compressed air are necessary. These causes an increase in cost of production equipment, leading to an increase in price of products.
To solve the foregoing subjects, the apparatus of the present invention should comprise deflection impartation means for deflecting one plate shaped substance located on the top of a plurality of stacked plate shaped substances; top plate shaped substance holding means for holding one uppermost plate shaped substance and separating the one uppermost plate shaped substance from other plate shaped substances, the one uppermost plate shaped substance being in a deflected state; and transporting means for transporting the one uppermost plate shaped substance which is separated from other plate shaped substances.
In such apparatus, when the one plate shaped substance located on the top of the plurality of stacked plate shaped substances is deflected, a deflection similarly occurs also in a plate shaped substance contacting with the under surface of the uppermost plate shaped substance. With this, restoring force to remove the deflection of the plate shaped substance contacting with the under surface of the uppermost plate shaped substance works. If the restoring force exceeds adhesive force acting between the uppermost plate shaped substance and the plate shaped substance under the uppermost plate-shapes object, the adherence of the uppermost plate shaped substance with the plate shaped substance under the uppermost plate shaped substance is dissolved, and the plate shaped substance under the uppermost plate shaped substance restores its original shape. In this case, if it is tried to separate the foregoing uppermost plate shaped substance from other plate shaped substances while keeping the deflection of the uppermost plate shaped substance, a re-attachment in the uppermost plate shaped substance can be prevented. Moreover, when it is tried to cause the foregoing deflection plural times, the attachment of the uppermost plate shaped substance to the plate shaped substance under the uppermost plate shaped substance can be dissolved more securely. Furthermore, to cause the deflection, it suffices that a load is applied to a portion of the uppermost plate shaped substance while mechanically constraining another portion of the uppermost plate shaped substance. In this case, as the way to apply the load, if the portion of the uppermost plate shaped substance is sucked by vacuum suction, flaws on the surface of the plate shaped substance can be prevented.
In the above described manner, without use of the spacer nor means for blowing the ionized air, the uppermost plate shaped substance among the stacked plate shaped substances can be separated and transported securely and cheaply.
Moreover, in the foregoing manufacturing apparatus, in order to try not to cause deformation and slippage during the step of curing the UV curable cationic composition after the two disc substrates are superposed while interposing the UV curable cationic composition therebetween, the following items are essential. Specifically, if the. deformation and the slippage occur in a state where the UV curable cationic composition spreads all over the plane between the two disc substrates, that is, in a state where the spreading thereof is completed, it is very difficult to dissolve the deformation and the slippage even if the UV curable cationic composition is not perfectly cured, and a deflection angle created in the disc substrate after the cure thereof is large. Accordingly, a countermeasure should be taken such that the deformation and the slippage are not caused while the UV curable cationic composition is spreading all over the plane between the two disc substrates, after the UV curable cationic composition is coated on disc substrate and the other disc substrate is superimposed thereon. When the manufacture of DVDs is considered, since the disc substrate is as thin as 0.6 mm and made of polycarbonate showing a low rigidity, a spreading step must be performed on a flat plane composed of a member showing a rigidity at a level that prevents the disc substrate from deformation due to its own weight.
The present invention based on such knowledge has a feature in that to allow the foregoing UV curable cationic composition to spread between the foregoing two disc substrates superposed upon another by the foregoing superimposing means, a statically placing plane for placing the foregoing disc substrates comprises.
Although it is essentially easy to prepare such statically placing plane, it is difficult to realize the statically placing plane in a space limited on actual production lines. This is because the preparation of the statically placing plane having a wide area, which statically places the DVDs to be mass-produced one by one, is not practical.
The DVDs includes a type of DVD in which a convex portion having a ring shape (a ring-shaped convex portion) is formed in an external periphery of a clamping area. Since this convex portion exists on an external surface of the DVD, when the DVDs are stacked, the ring-shaped convex portions existing upper and lower external surfaces contact the ring-shaped convex portions of the adjacent DVDs, so that the disc surfaces of the DVD cannot be contacted with those of the DVDs adjacent thereto. Accordingly, the DVD having a low rigidity is deformed into an umbrella shape, that is, deflected, by its own weight or by a weight of the DVD stacked thereon.
There is also a type of DVD in which the convex portion is not formed, and deformation owing to existence of the convex shaped ring does not occur. However, if the number of DVDs stacked becomes large, minute deformations are accumulated, and there is a fear that the deformations of the DVDs positioned at an upper portion of the stacked DVDs cannot be neglected from the viewpoint of a product specification.
To realize the statically placing plane in a limited space, it is conceived that a rigid disc having a flat plane, for example, a disc made of Al, is interposed between the stacked discs.
Accordingly, the present invention has a feature in that stacking means for stacking the plurality of discs upon another; and rigid disc placing means for placing a rigid disc having a flat plane on the foregoing disc during a step for stacking the plurality of discs upon another. Moreover, a material of the rigid disc is not especially limited as long as the object is achieved. However, since it is also assumed that the stacked DVDs are transported to other places, the material of the DVD should be light for the convenience of the transportation. Generally, since the smaller specific gravity a material has, the lower rigidity the material shows, the disc must have a considerable thickness to achieve the object as the rigid disc. For example, polycarbonate which is the same material as that of the disc substrate of the DVD, can be used. In this case, the thickness of the rigid disc must be determined so as to have a sufficient rigidity. A metal material can be used as the rigid disc, and alumium and titanium having a small specific gravity are preferable in this case.
Here, in the case where a type of a DVD without the convex ring formed is applied to, a rigid disc having a simple flat plane is satisfactorily used. In the case of the DVD with the convex ring formed, consideration for forming a ring-shaped groove in a portion of the rigid disc corresponding to the ring-shaped convex portion is necessary. Flatness of the flat plane is not especially limited as long as a deflection is within a predetermined range of value, and it suffices that the flatness is experimentally determined in accordance with conditions of the spreading and the like. Moreover, the flat plane needs not to be an entirely continuous plane, and an intermittent flat plane is well adopted as long as the desired objects can be achieved. For example, an intermittent flat plane in which ring-shaped members having different diameters are arranged coaxially may be adopted, and the flat plane which is here described is a concept including these constitutions.
In such apparatus, since the spreading is performed on the statically placing plane, occurrence of the deflection can be controlled.
After the UV curable cationic composition is spread, the disc may be left until resin is completely cured. However, in consideration for productivity, the disc should be transported to other places. Since the UV curable cationic composition is in an uncured state for a while immediately after the spreading, the two disc substrates shift relatively from each other unless the two disc substrates are transported with considerable caution. Moreover, there is also a problem that the UV curable cationic composition protruded from the external peripheral end of the disc that is a superposition object is sticky, and tractability is poor.
The inventor made the investigation about this point, and obtained knowledge that even in the UV curable cationic composition, the cure thereof is promoted extremely when ultraviolet ray having illuminance of a predetermined level or more is radiated thereonto for a short period of time. As means for radiating the ultraviolet ray of a predetermined level or more for a short period of time, it was ascertained that flashing ultraviolet radiation using a flash lamp is effective. At this time, the ultraviolet radiation may be performed satisfactorily in such manner that the ultraviolet ray is concentrated not on the surface of the disc substrate but on the external peripheral end thereof. In the case where the ultraviolet ray is radiated onto the external peripheral end concentratedly, adverse effects owing to heat from a lamp light source scarcely become problems. The apparatus of the present invention has a feature in that a second ultraviolet radiation means for radiating ultraviolet rays onto each external peripheral end of the plurality of stacked discs is provided. With such constitution, the UV curable cationic composition at the external peripheral ends of the two disc substrates is cured in early stages, so that the problem of stickiness is dissolved and the slippage between the two disc substrates occurred in transporting the disc substrates can be prevented.
When the UV curable cationic composition near the external peripheral end of the disc is cured by further radiating the ultraviolet ray onto the external peripheral end thereof, as above-described, efficiency is bad when the ultraviolet radiation is performed for the discs one by one. Accordingly, the plurality of discs are stacked, and the ultraviolet radiation may be satisfactorily performed for an aggregation of the stacked discs. By such ultraviolet radiation, it is possible to perform the end curing treatment for a lot of discs at a time. Moreover, the plurality of discs should rotate around a central axis obtained by connecting the centers of the discs when the ultraviolet ray is radiated by the second ultraviolet radiation means. Thus, the ultraviolet rays can be easily radiated onto the external peripheral ends of all the discs uniformly.
The second ultraviolet radiation means should adopt a flashing type in terms of energy efficiency.
The above-described effects can be exerted only by the cationic polymerization photoinitiator, and hence exerted also by the light initiator combined with the cationic polymerization photoinitiator. The curing promotion effect can be improved by this action.
Besides the methods for radiating the ultraviolet rays in the above-described manners, there is also a method to apply a heat to a predetermined temperature. In this case, a constitution, in which a heating means for performing a heating treatment for the plurality of stacked discs is provided, suffices. Since the technique to heat the discs can be satisfactorily performed by cheaper equipment compared to that necessary for the ultraviolet radiation, this technique is effective for reduction of production cost. Although a heat temperature must be decided appropriately in accordance with a material constituting the disc substrates and UV curable cationic composition, the heat temperature should be set to 70xc2x0 C. or less in the case of the DVD because of a possibility that a deformation of the disc substrate may occur due to a thermal stress at a temperature above 70xc2x0 C. Moreover, to promote the cure of the UV curable cationic composition, the heating temperature should be set to a temperature of 40xc2x0 C. or more.
As the apparatus for the heat treatment, though a heater using the most prevailing heating wire heater can be used, it is preferable in consideration for heating performance that a heater using a halogen heater is used. Specifically, compared to heaters including the heating wire heater, a quartz heater, a ceramics heater and the like, since the halogen heater reaches to a predetermined temperature in a short time after starting the heating, the halogen heater can perform the heat treatment quickly.
As the halogen heater, the one publicly known and commonly used can be used, and a halogen heater with a reflection film capable of radiating energy toward one direction effectively should be used.
This heat treatment should be performed at least for whole the end of the disc. Moreover, to make the deflections of the individual discs as little as possible, it is preferable that each disc is heated so that the entire surface thereof is made to equal in temperature uniformly. To achieve this, each disc can be left for a determined period of time in, for example, a temperature controlled chamber which controlled to a predetermined temperature by a heater. A plurality of heaters having directivity may be provided such that the heaters do not contact the outside of the disc and surround the entire end of the disc. However, only one heater is preferably used, and the heater and the disc are disposed so that the heater and the disc do not contact with each other. The heat treatment should be performed while rotating only the disc and the heater is fixed. Although a rotation speed of the disc at this time is not especially limited, in terms of productivity, the rotation speed should be selected at a range of, for example, 20 to 200 rpm. A distance between the heater and the end of the disc can be appropriately selected depending on sorts of substrate materials constituting the disc and a thickness thereof, and a power of the heater, and is within a range of 1 to 100 cm, ordinarily. The distance should be 10 to 70 cm in terms of space saving. When the heater power is high, it suffices that the distance between the heater and the disc is made to be larger. In some cases, it is also possible to allow only the heater to rotate along the end of the disc without rotating the disc such that the heater does not touch the disc. The heat treatment should be performed for a period of time until the end of the disc is completely cured. The time of the treatment is 1 to 15 minutes, ordinarily, and especially should be 3 to 10 minutes in terms of productivity.
As described above, by performing the heat treatment after the superposition of the discs, the stickiness of the UV curable cationic composition protruding from the external periphery end of the disc after the superposition can be suppressed, and the cure of the UV curable cationic composition is promoted. Thus, the performance of the heat treatment after the superposition can contribute to production efficiency.
By the way, in manufacturing such disc, as the method for transporting the disc, a method is used widely, in which adsorption means such as vacuum suction is provided in a tip of an arm so as to hold one surface of the disc by suction, and the disc is transported by allowing the arm to perform turning movement. However, in any case where one of the above described methods is used, when the discs which are stuck with each other and form a unit are transported to the ultraviolet radiation step, the cure of the adhesive between the two discs substrates is not completed yet. For this reason, there has been a fear that a central axis deviation may occur in the disc substrate that is not firmly held by the adsorption means, because of influences such as centrifugal force and acceleration in the transportation. Since the disc, which caused the central axis deviation cannot be used, such disc is scrapped as defectives.
To reduce the influences such as the centrifugal force and the acceleration, applied to the disc substrate which is not held firmly in the transportation, it is conceived that such influences can be effectively reduced by lowering a transportation speed. However, a problem of a lowering of productivity occurs.
Accordingly, in the apparatus of the present invention, it suffices that holding means for holding discs; axis alignment means for allowing positions of inner wall planes of hole portions formed in the foregoing two disc substrates to be coincident with each other; and movement means for moving the foregoing holding means and the foregoing axis alignment means simultaneously are provided. At this time, the foregoing axis alignment means should be diameter enlargement/reduction means.
Specifically, the holding means holds the discs which are stuck, and the axis alignment means performs the central axis alignment by allowing the positions of the inner wall planes of the hole portions formed in the two disc substrates to be coincident with each other. In this state, the movement means moves the holding means and the axis alignment means simultaneously, and hence the discs can be transported in a stage where the adhesive is not cured. Accordingly, until the adhesive is cured, the discs need not to be statically placed at the place where the discs are to be stuck, and the adhesion of the disc substrates can be effectively performed. Thus, production efficiency of the discs can be increased.
Furthermore, to allow the axes of the two disc substrates to be coincident with each other, conceived are a method in which external periphery portions of the substrates are allowed to be coincident with each other and a method in which positions of hole portions provided at the centers of the principal surfaces of the substrates are allowed to be coincident with each other. The method to allow the positions of the hole portions to be coincident with each other can cope easily with a case where a size of the disc substrate changes. Moreover, when the disc substrate is thin, a deflection and a strain may occur in the disc substrate by applying force to the external periphery portion of the substrate for positioning. However, since the hole portion is formed so as to be smaller compared to a size of the disc and will be hardly deformed with an application of force, the positioning is performed easily.
As the axis alignment means, diameter enlargement/reduction means should be used, and specifically an air picker or a chuck should be used. The chuck is essentially a tool which seizes work pieces and the like by opening and shutting several nails. It is possible to press the inner wall plane of the hole portion formed in the disc substrate by utilizing the opening of the nail.